Semiconductor device comprising string structures formed on active region

ABSTRACT

A semiconductor device having a string gate structure and a method of manufacturing the same suppress leakage current. The semiconductor device includes a selection gate and a memory gate. The channel region of the selection gate has a higher impurity concentration than that of the memory gate. Impurities may be implanted at different angles to form the channel regions having different impurity concentrations.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Divisional of U.S. application Ser. No. 12/555,830, filed Sep.9, 2009, which claims priority under 35 U.S.C §119 to Korean PatentApplication No. 10-2008-0093774, filed on Sep. 24, 2008, the entirety ofwhich is herein incorporated by reference.

BACKGROUND OF THE INVENTIVE CONCEPT

1. Field of the Inventive Concept

The present inventive concept relates to semiconductor devices and tomethods of manufacturing the same. More specifically, the presentinventive concept relates to a semiconductor device having a string ofgates including (string and ground) selection gates and a group memorygates interposed between the selection gates, and to a method ofmanufacturing the same.

2. Description of Related Art

A transistor, which is a unit of a semiconductor device, includes a gateelectrode formed on a semiconductor substrate and source/drain regionsformed in the semiconductor substrate at opposite sides of the gateelectrode. A channel extending through the semiconductor substrateconnects the source/drain regions across the gate electrode. Thesource/drain regions are doped with impurities of a conductivity typedifferent from the conductivity type of the impurities of thesemiconductor substrate. For example, in a transistor in which thesemiconductor substrate contains N-type impurities, the source/drainregions are doped with P-type impurities.

The elements of such transistors are being scaled down to meet thegrowing demand for high-density semiconductor devices. In this respect,the length of the channel of the gate electrode is becoming smaller.However, a transistor having a small channel length is prone to what areknown in the art as short-channel effects. These effects reduce thereliability of the semiconductor device.

SUMMARY OF THE INVENTIVE CONCEPT

Accordingly, an object of the present inventive concept is to provide ahigh-density semiconductor device that is capable of operating stably.

According to one aspect of the present invention, there is provided asemiconductor device with a ground selection gate and a string selectiongate disposed on an active region of a substrate, memory gates disposedbetween the ground selection gate and the string selection gate, andwherein the channels of the selection gates have a higher concentrationof impurities than the channel of at least one of the memory gates.

The active region is thus made up of selection channel regions below theground selection gate and the string selection gate, respectively, and amemory cell region which is located beneath the memory gates and bordersthe selection channel regions so as to terminate at locations directlybeneath sidewalls of the selection gates. The memory cell region is inturn made of memory channel regions below the memory gates,respectively. At least a portion of each of the selection channelregions has a higher concentration of an impurity than at least one ofthe memory channel regions.

The memory cell region is also made up of memory impurity regions atopposite sides of each of the memory channel regions. The aforementionedat least one of the memory channel regions and the unit memory impurityregions adjacent thereto may have the same conductivity type. Accordingto another aspect of the inventive concept, there is provided a methodof fabricating a semiconductor device comprising forming a pair ofselection gates and a group of memory gates between the selection gateson the active region of a substrate, and doping the active region insuch a way and in such a sequence relative to the forming of the gatesas to produce doped selection regions below the selection gates in whichthe doped selection regions have a higher concentration of impuritiesthan in the active region below the memory gates. Also, the doping iscarried out such that the doped selection regions, and those portions ofthe active region adjacent to opposite sides of at least one of thememory gates, are of the same conductivity type as the active regionbelow the memory gates.

According to another aspect of the inventive concept, there is provideda method of fabricating a semiconductor device comprising selectivelyforming impurity-implanted regions in an active region having impuritiesat a first impurity concentration, and forming a ground selection gate,a string selection gate, and memory gates on the active region. Thegates are formed so that memory gates are disposed between the groundselection gate and the string selection gate. Also, the ground selectiongate and the string selection gate are disposed on theimpurity-implanted regions, respectively. The impurity-implanted regionshave a concentration of impurities greater than the first impurityconcentration. Also, the active region between the ground selection gateand the string selection gate has the first impurity concentration, andthe impurities of the first impurity concentration and the secondimpurity concentration are of the same conductivity type

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor device according to the presentinvention.

FIGS. 2, 3 and 4 are cross-sectional views illustrating a semiconductordevice according to some embodiments of the present inventive conceptand a method of manufacturing the same.

FIGS. 5, 6 and 7 are cross-sectional views illustrating a semiconductordevice according to other embodiments of the present inventive conceptand a method of manufacturing the same.

FIGS. 8, 9 and 10 are cross-sectional views illustrating a semiconductordevice according to other embodiments of the present inventive conceptand a method of manufacturing the same.

FIGS. 11, 12, 13 and 14 are cross-sectional views illustrating asemiconductor device according to other embodiments of the presentinventive concept and a method of manufacturing the same.

FIGS. 15, 16, 17 and 18 are cross-sectional views illustrating asemiconductor device according to other embodiments of the presentinventive concept and a method of manufacturing the same.

FIGS. 19, 20, 21 and 22 are cross-sectional views illustrating asemiconductor device according to other embodiments of the presentinventive concept and a method of manufacturing the same.

FIGS. 23, 24 and 25 are cross-sectional views illustrating asemiconductor device according other embodiments of the presentinventive concept and a method of manufacturing the same.

FIG. 26 is a block diagram of an electronic system including asemiconductor device according to some embodiments of the presentinvention.

FIG. 27 is a block diagram of a memory system including a semiconductordevice according to some embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventive concept will now be described more fullyhereinafter with reference to the accompanying drawings. Like numbersdesignate like elements throughout the drawings. Thus, detaileddescriptions of elements of a semiconductor device which are similar tothose already described in connection with a previous embodiment, andwhich elements are designated by like reference numerals, may be omittedfor the sake of brevity. The same goes for the process or processes offabricating such elements. Also, the dimensions of layers and regionsmay be exaggerated in the drawings for ease of illustration.

A first embodiment of a semiconductor device according to the presentinventive concept will now be described below in detail with referenceto FIGS. 1 and 2.

A semiconductor device according to the present inventive concept has asubstrate 110 in which active regions ACT are provided, and at least onestring of gates disposed in a first direction D1 across each activeregion ACT of the substrate 110. The string of gates includes a pair ofselection gates and a group of memory gates MG memory gates interposedbetween the selection gates. The pair of selection gates includes aground selection gate GSG and a string selection gate SSG. Spacers (notshown) may be disposed on sidewalls of the gates GSG, SSG, and MG.

The memory gates MG comprise a first memory insulating layer 141, afirst memory gate layer 143, a second memory insulating layer 145, and asecond memory gate layer 147. The first memory gate layer 143 is acharge storage layer such as a floating-type storage layer or atrap-type storage layer.

Preferably, the second memory insulating layer 145 includes a film ofmaterial selected from the group consisting of silicon oxide(Si_(x)O_(y)), aluminum oxide (Al_(x)O_(y)), tantalum oxide(Ta_(x)O_(y)), hafnium oxide (HfO₂), hafnium aluminum oxide (HfAlO), andhafnium silicon oxide (HfSiO). Furthermore, the second memory insulatinglayer 145 may be formed of a plurality of films of material, asdisclosed in U.S. Patent Publication No. 2006/0180851, the entirety ofwhich is hereby incorporated by reference. Also, the dielectric constantof the second memory insulating layer 145 may be greater than that ofthe first memory insulating layer 141 as disclosed in U.S. Pat. No.6,858,906 the entirety of which is also hereby incorporated byreference.

The second memory gate layer 147 may have a work function of at least 4eV as disclosed in U.S. Pat. No. 7,253,467 the entirety of which is alsohereby incorporated by reference.

The ground selection gate GSG includes a first ground insulating layer131, a first ground gate layer 133, a second ground insulating layer135, and a second ground gate layer 137 electrically connected to thefirst ground gate layer 133. The string selection gate SSG includes afirst string insulating layer 151, a first string gate layer 153, asecond string insulating layer 155, and a second string gate layer 157electrically connected to the first string gate layer 153.Alternatively, the ground selection gate GSG has only one groundinsulating layer and ground gate layer, and the string selection gateSSG has only one string insulating layer and string gate layer.

In the present embodiment, the second ground gate layer 137 of theground selection gate GSG extends in a second direction D2, running atan angle relative to the first direction D1, so as to constitute aground selection line GSL. The second string gate layer 157 of thestring selection gate SSG extends in the second direction D2 toconstitute a string selection line SSL. The second memory gate layers147 of the memory gates MG extend in the second direction D2 toconstitute wordlines WL.

In the present embodiment, each active region ACT in the semiconductorsubstrate 110 comprises a well having regions 112 in which impuritiesare implanted. The impurity-implanted regions 112 are located below andbetween the ground selection gate GSG and the adjacent ground selectiongate GSG′, and below and between the string selection gate SSG and theadjacent string selection gate SSG′, respectively.

More specifically, impurities are implanted into selection channelregions 116, selection impurity regions 117, and a memory cell region118 of the substrate.

The selection channel regions 116 are those regions (in the well) belowand bounded between the sides of each of the ground selection gate GSGand the string selection gate SSG, respectively. The memory cell region118 is that region which extends (in the well) between the groundselection gate GSG and the string selection gate SSG. Furthermore, theselection impurity regions 117 are those regions (in the well) betweenthe ground selection gate GSG and an adjacent ground selection gate GSG′and between the string selection gate SSG and an adjacent stringselection gate SSG′, respectively.

The selection channel regions 116 and the memory cell region 118 havethe same conductivity type, and at least a portion of each of theselection channel regions 116 contains a higher concentration ofimpurities than the memory cell region 118. Thus, each of the selectionchannel regions 116 contains a higher concentration of impurities thanthe channel regions beneath the memory gates MG including those closestto the selection channel regions 116 in the string.

A method of manufacturing a semiconductor device of FIG. 2 according tothe present inventive concept will now be described below in detail withreference to FIGS. 1 through 4.

Referring first to FIGS. 1 and 3, a device isolation layer (not shown)is formed on a substrate 110 to define an active region ACT extendinglongitudinally in a first direction D1. An upper portion of the activeregion ACT, e.g., a well, contains impurities at a first concentration.

An impurity implanting mask 120 is formed on the substrate 110 includingover the active region ACT. The impurity implanting mask 120 hasopenings 122 that expose regions to be implanted. The impurityimplanting mask 120 comprises an insulating material such as aphotoresist, silicon nitride or silicon oxide.

Impurities are implanted into the active region ACT of the substrate 110using the impurity implanting mask 120. At this time, impurity-implantedregions 112 are formed in those parts of the active region ACT exposedby the openings 122. The concentration of impurities in the implantedregions 112 is higher than the concentration of impurities in the otherportions of the active region ACT but the impurity-implanted regions 112are of the same conductivity type as the other portions of the activeregion ACT.

Referring to FIG. 4, the impurity implanting mask 120 is removed. Afirst insulating layer 121, a first gate layer 123, a second insulatinglayer 125, and a second gate layer 127 are then formed on the substrate110. The first insulating layer 121 may comprise silicon oxide, and thesecond insulating layer 125 may comprise a film of silicon oxide and/ora film of silicon nitride. Preferably, the second insulating layer 125includes a high-k dielectric material. The first gate layer 123 maycomprise conductive polysilicon. Alternatively, the first gate layer 123comprises a layer of high-k dielectric material. The second gate layer127 preferably comprises one or more films selected from the groupconsisting of conductive polysilicon, metal, metal silicide andconductive metal nitride.

Before the second gate layer 127 is formed, a butting region (not shown)may be formed by selectively etching the second insulating layer 125 toform (butting) openings that expose the first gate layer 123 at theregions where the ground selection gate GSG and the string selectiongate (SSG) are to be formed (refer to FIG. 2). Then, the (butting)openings are filled when the second gate layer 127 is formed on thesecond insulating layer 125. As a result, the second gate layer 127contacts (i.e., is stacked directly on) the first gate layer 123 at theregions where the ground selection gate GSG and the string selectiongate SSG are to be formed.

Then, the layers 121, 123, 125 and 127 are etched to form at least apair of selection gates, including a ground selection gate GSG and astring selection gate SSG, and a set of memory gates MG therebetween onthe substrate 110. In addition, a common source line CSL may be formedbetween the ground selection gate GSG and an adjacent ground selectiongate GSG′. Also, a DC plug may be formed between the string selectiongate SSG and an adjacent string selection gate SSG′ as electricallyconnected to a bitline BL.

Another embodiment of a semiconductor device according to the presentinventive concept will now be described below in detail with referenceto FIGS. 1 and 5.

A ground selection gate GSG and a string selection gate SSG, and memorygates MG interposed therebetween, are disposed on a substrate 110 havingan active region ACT. The gates GSG, SSG, and MG are similar to thosedescribed above in connection with the embodiment of FIG. 2.

Selection channel regions 116 are defined (in the well) in the substratebelow the ground selection gate GSG and the string selection gate SSG,respectively, and a memory cell region 118 extends (in the well) in thesubstrate between the ground selection gate GSG and the string selectiongate SSG. Furthermore, selection impurity regions 117 extend (in thewell) in the substrate between the ground selection gate GSG and anadjacent ground selection gate GSG′ and between the string selectiongate SSG and an adjacent string selection gate SSG′, respectively.

The selection channel region 116 and the memory cell region 118 are ofthe same conductivity type, but the concentration of impurities in atleast a portion of the selection channel regions 116 is higher than theconcentration of impurities in the memory cell region 118. To this end,as will be described below, the channel regions 116 may be formed asimpurity-implanted regions 114 of the substrate.

A method of manufacturing the semiconductor device of FIG. 5 accordingto the present inventive concept will now be described below in detailwith reference to FIG. 1 and FIGS. 5 through 7.

Referring to FIG. 6, an impurity implanting mask 124 is formed on asubstrate 110 including over the active region ACT having impurities ata first concentration. The impurity implanting mask 124 has openings 126exposing the substrate 110. In particular, the openings 126 exposelocations on the active region where ground selection gates (GSG andGSG′) and string selection gates (SGS and SGS′) are to be formed (FIG.5). The impurity implanting mask 124 is of an insulating material suchas a photoresist, silicon nitride or silicon oxide.

Impurities are implanted into the active region of the substrate 110using the impurity implanting mask 124. At this time, impurity-implantedregions 114 are formed in those parts of the active region exposed bythe openings 126.

The concentration of the impurities in the impurity-implanted regions114 is higher than the concentration of impurities in other portions ofthe active region ACT, but the impurity-implanted region 114 has thesame conductivity type as the other portions of the active region ACT.

The impurity implanting mask 124 is then removed. Then, a groundselection gate GSG and a string selection gate SSG and memory gates MGare formed on the substrate 110. The gates GSG, SSG, and MG are formedsimilarly to those described above in connection with the embodiment ofFIGS. 1-4.

Alternatively, referring to FIG. 7, an impurity implanting mask 128 isformed on the substrate 110. The impurity implanting mask 128 hasopenings 129 that expose portions of the active region of the substrate,and the impurity implanting mask 128 covers locations corresponding tothe memory cell region 118 and portions of the selection channel regions116 that border the memory cell region 118. Thus, the openings 129expose locations corresponding to the selection impurity regions 117 andportions of the selection channel regions 116 that border each of theselection channel regions 117.

Impurities are implanted into the active region using the impurityimplanting mask 128 as an ion implantation mask. The impurities areimplanted at an implantation angle θi relative to the upper surface ofthe substrate 110 and so as to have a concentration (secondconcentration) greater than the concentration (first concentration) ofimpurities in the other portions of the substrate. The implantationangle θi may be selected based on the height (Hi) of the impurityimplanting mask 128 and the difference (Di) between the width of theopening 129 in the impurity implanting mask 128 and the desired width ofthe region over which impurities are to be implanted in the portion ofthe substrate 110 exposed by the opening 129. Thus, the implantationangle θi can be expressed as: tan⁻¹(Hi/Di). As a result, animpurity-implanted region 114 is formed in only a portion of the activeregion ACT exposed by the opening 129. Also, due to the implantationangle θi, the impurity-implanted region 114 extends below the impurityimplanting mask 128. That is, the selection channel regions 116 have thesecond impurity concentration. The second impurity concentration ishigher than the first impurity concentration, but the impurity-implantedregions 114 are of the same conductivity type as the other portions ofthe active region ACT below the impurity implanting mask 128.

Another embodiment of a semiconductor device according to the presentinventive concept will now be described below in detail with referenceto FIGS. 1 and 8.

A string of gates is disposed on an active region ACT of a semiconductorsubstrate 110. The gates include a ground selection gate GSG, a stringselection gate SSG, and memory gates MG interposed therebetween on thesubstrate 110. The gates GSG, SSG, and MG are similar to those describedabove in the embodiments of FIGS. 2 and 5. Also, the substrate 110 has awell constituting the active region ACT, and in the well there areprovided selection channel regions 116, selection impurity regions 117,and a memory cell region 118 as described above.

The selection channel regions 116, the selection impurity regions 117,and the memory cell region 118 have the same conductivity type. Also, atleast a portion of each of the selection channel regions 116 has ahigher concentration of impurities than the memory cell region 118.

In particular, a respective impurity-implanted region 119 having ahigher concentration of impurities than the other parts of the activeregion ACT is disposed below each of the sidewalls of the selectiongates GSG and GSG″ that face each other, and the sidewalls of theselection gates SSG′ and SSG′ that face each other. That is, each of theimpurity-implanted regions 119 is spread over a selection channel region116 and a selection impurity region 117.

A method of manufacturing the semiconductor device of FIG. 8 accordingto the present inventive concept will now be described below in detailwith reference to FIG. 1 and FIGS. 8 through 10.

Referring to FIGS. 1, 8 and 9, at least a pair of selection gatesincluding a ground selection gate GSG and a string selection gate SSG,and memory gates MG are formed on an active region of a substrate 110.The gates are formed as described above in connection with the previousembodiments. As was also described above, the gates demarcate selectionchannel regions 116, selection impurity regions 117 and a memory region118.

Referring to FIG. 10, impurities are implanted by an ion implantationprocess and more specifically, by an oblique ion implantation process,into the active region using the gates GSG, SSG, and MG as an ionimplantation mask. The oblique ion implantation process implantsimpurities into the substrate at a predetermined implantation angle θisuch that impurity implanted regions 119 are formed in the active regionof the substrate 110. One impurity implanted region 119 extends belowone side portion of the ground selection gate GSG and into part of thesubstrate adjacent to the ground selection gate GSG, and anotherimpurity implanted region 119 extends below one side portion of thestring selection gate SSG and into part of the substrate adjacent to thestring selection gate SSG. In particular, impurities are selectivelyimplanted into the active region at the boundaries between theimpurity-implanted regions 117 and the selection channel regions 116. Atthis time, impurities are not implanted into the active region betweenthe memory gates MG, between the set of memory gates MG and the groundselection gate GSG, and between the set of memory gate MG and the stringselection gate SSG. The implantation angle θi is smaller than a firstangle θ1 and greater than a second angle θ2 (i.e., θ2<θi<θ1).

The first angle θ1 is based on the distance d1 between an a pair ofadjacent gates including a memory gate MG and the a selection gate GSGor SSG, and the height h1 of the structure used as a mask during theimplantation process, namely, the height of the selection gates. Inparticular, the first angle θ1 may be the minimum angle at which theimpurities can be implanted into the active region between the memorygate MG and the adjacent selection gate GSG or SSG.

The second angle θ2 is based on the distance d2 between the adjacentstring selection gates SSG and SSG′ (or the adjacent ground selectiongates GSG GSG′) and the height h1. In particular, the second angle θ2 isthe minimum angle at which the impurities can be implanted into theactive region between the adjacent string selection gates SSG and SSG′(or the adjacent ground selection gates GSG GSG′).

Alternatively, an impurity implanting mask (not shown) may be formed tocover the substrate 110 between the selection gates GSG and SSG duringthe ion implantation process. In this case, the active region betweenthe adjacent ground selection gates GSG and GSG′ is exposed by theimpurity implanting mask. The impurities are implanted into the exposedregion of the substrate 110 at an implantation angle θi greater than thesecond angle θ2 and less than 90 degrees (i.e., θ2 <θi<90°). Theimpurity implanting mask may be a patterned layer of photoresist orspacers formed on sidewalls of the gates GSG, SSG, and MG. Such animpurity implanting mask is disclosed in U.S. Patent Publication No.2006/0220098, the entirety of which is hereby incorporated by reference.

In any case, the impurity-implanted regions 119 are formed at theboundary between the selection channel regions 116 and the selectionimpurity regions 117. That is, impurities at a higher concentration thanin the other portions of the active region below the string may belocally implanted in the selection channel region 116.

Then, an annealing process may be performed to expand theimpurity-implanted regions 119 (as shown in FIG. 8).

Another embodiment of a semiconductor device according to the presentinventive concept will be described below in detail with reference toFIGS. 1 and 11.

This embodiment is similar to that of FIG. 8 except that a first dopingregion 111 extends along the upper portion of the active region ACTincluding through the selection channel regions 116, the selectionimpurity region 117, and the memory cell region 118. Theimpurity-implanted regions 119 are thus second doping regions and havethe same conductivity type as the first doping region 111; however, theconcentration of impurities in the impurity-implanted regions 119(second doping regions) is higher than in the first doping region 111.Thus, the concentration of impurities in at least a portion of each ofthe selection channel regions 116 (which portion is referred to as aselection doping region) is higher than in the memory cell region 118.

A method of manufacturing the semiconductor device of FIG. 11 accordingto the present inventive concept will now be described below in detailwith reference to FIG. 1 and FIGS. 11 through 14.

Referring to FIGS. 1 and 12, a first impurity implanting process isperformed to implant impurities at a first concentration into an activeregion of a substrate 110. As a result, a first doping region 111 isformed in the well at the upper surface of the active region ACT of thesubstrate 110. Thus, the selection channel regions 116, the selectionimpurity regions 117, and the memory cell region 118 each will initiallyhave a layer of impurities at the first concentration.

Referring to FIG. 13, gates GSG, SSG, and MG are formed as describedabove in connection with the previous embodiments. Accordingly,selection channel regions 116, selection impurity regions 117 and amemory cell region 118 are demarcated.

Referring to FIG. 14, a second impurity implanting process is performedas described above in connection with the embodiment of FIGS. 9 and 10.That is, an oblique ion implanting process may be performed using thegates GSG, SSG, and MG as a mask (or an ion implanting mask as disclosedin U.S. Patent Publication No. 2006/0220098 may be used). In any case,the impurities used in the second impurity implanting process have thesame conductivity type as those used in the first impurity implantingprocess.

As a result, impurity-implanted regions 119 are formed at the boundariesbetween the selection channel regions 116 and the selection impurityregions 117. The impurity-implanted regions 119 have impurities at aconcentration higher than the first impurity concentration.

Referring to FIG. 11, an annealing process is carried out to expand theimpurity-implanted regions 119.

Another embodiment of a semiconductor device according to the presentinventive concept will now be described below in detail with referenceto FIGS. 1 and 15.

A ground selection gate GSG, a string selection gate SSG, and memorygates MG are disposed on an active region ACT of a substrate 110. Thegates GSG, SSG, and MG are similar to those of the above-describedembodiments. Thus, the substrate 110 has selection channel regions 116below the ground selection gate GSG and below the string selection gateSSG, respectively, a memory cell region 118 between the ground selectiongate GSG and the string selection gate SSG, and selection impurityregions 117 between the adjacent ground selection gates GSG and GSG′ andbetween the adjacent string selection gates SSG and SSG′, respectively.

First doping regions 113 having impurities at a first impurityconcentration are disposed (in the well) in the substrate 110 betweenadjacent ones of the gates GSG, SSG, and MG, respectively. The firstdoping regions 113 may extend to locations below the gates GSG, SSG, andMG, as well. Second doping regions 119 are disposed below each of theconfronting sidewalls of the adjacent string selection gates SSG andSSG′ and each of the confronting sidewalls of the adjacent groundselection gates GSG and GSG′, respectively. The second doping regions119 have the same conductivity type as the first doping regions 113, butthe concentration of impurities in the second doping regions 119 (secondimpurity concentration) is higher than the concentration of impuritiesin the first doping regions 113 (first impurity concentration).

Thus, the concentration of impurities in at least a portion of each ofthe section channel regions 116 is higher than the concentration ofimpurities in the memory cell region 118.

A method of manufacturing the semiconductor device of FIG. 15 accordingto the present inventive concept will now be described below in detailwith reference to FIG. 1 and FIGS. 15 through 18.

Referring to FIGS. 1 and 16, at least a pair of selection gatesincluding a ground selection gate GSG and a string selection gate SSG,and memory gates MG are formed on an active region of a substrate 110.The gates are formed as described above in connection with the previousembodiments. As was also described above, the gates demarcate selectionchannel regions 116, selection impurity regions 117 and a memory region118. Then, a first impurity implanting process is performed using thegates GSG, SSG, and MG as masks. As a result, first doping regions 113having impurities at a first concentration are formed in the substrate110 between the gates GSG, SSG, and MG.

Referring to FIG. 17, an annealing process is carried out to expand thefirst doping regions 113. Due to the annealing process, the first dopingregions 113 occupy portions of the substrate 110 below the memory gatesMG and the selection gates GSG and SSG.

Referring to FIG. 18, a second ion implanting process (an obliqueimpurity implanting process) is performed using the gates GSG, SSG, andMG as masks. The oblique ion implanting process may be performed in amanner similar to that described above (i.e., using the gates as a maskor using an ion implanting mask to cover the active region between thestring selection gate SSG and the ground selection gate GSG). Theimpurities used in the second ion implanting process have the sameconductivity type as those used in the first ion implanting process. Asa result, the second doping regions 119 are formed at the boundariesbetween the selection channel regions 116 and the selection impurityregions 117.

Referring to FIG. 15 again, an annealing process is then performed toexpand the second doping regions 119.

Thus, the concentration of impurities in at least a portion of theselection channel region 116 is greater than in the active region belowthe memory gates MG in the string.

Another embodiment of a semiconductor device according to the presentinventive concept will now be described below in detail with referenceto FIGS. 1 and 19.

A ground selection gate GSG, a string selection gate SSG, and memorygates MG are disposed on an active region ACT of a substrate 110. Thegates GSG, SSG, and MG are similar to those of the above-describedembodiments. Thus, the substrate 110 has selection channel regions 116below the ground selection gate GSG and below the string selection gateSSG, respectively, a memory cell region 118 between the ground selectiongate GSG and the string selection gate SSG, and selection impurityregions 117 between the adjacent ground selection gates GSG and GSG′ andbetween the adjacent string selection gates SSG and SSG′, respectively.

First doping regions 115 are disposed below the sidewalls of the gatesGSG, SSG, and MG, respectively. Each of the first doping regions 115 mayalso extend to a location below a respective one of the gates GSG, SSG,and MG. Second doping regions 119 are disposed below each of theconfronting sidewalls of the adjacent string selection gates SSG andSSG′ and each of the confronting sidewalls of the adjacent groundselection gates GSG and GSG′, respectively. The second doping regions119 have the same conductivity type as the first doping region 115, butthe concentration of impurities in the second doping regions 119 (secondimpurity concentration) is higher than the concentration of impuritiesin the first doping regions 115 (first impurity concentration).

Thus, the concentration of impurities in at least a portion of each ofthe section channel regions 116 is higher than the concentration ofimpurities in the memory cell region 118.

A method of manufacturing the semiconductor device of FIG. 19 accordingto the present inventive concept will now be described below in detailwith reference to FIG. 1 and FIGS. 19 through 22.

Referring to FIGS. 1 and 20, at least a pair of selection gatesincluding a ground selection gate GSG and a string selection gate SSG,and memory gates MG are formed on an active region of a substrate 110.The gates are formed as described above in connection with the previousembodiments. As was also described above, the gates demarcate selectionchannel regions 116, selection impurity regions 117 and a memory region118.

Then, a first impurity implanting process (an oblique impurityimplanting process) is performed using gates GSG, SSG, and MG as masks.The implantation angle θi of the impurity implanting process is equal toa first angle θ1 selected based on the distance d1 between a memory gateMG and the selection gate GSG or SSG adjacent thereto and the height h1of the selection gate GSG or SSG. More specifically, as is clear fromthe description of previous embodiments and as shown in the figure, thefirst angle θ1 may be tan⁻¹ (h1/d1).

Due to the first impurity implanting process, first doping regions 115are formed below sidewalls of the memory gates MG and sidewalls of theselection gates GSG and SSG, respectively.

Referring to FIG. 21, an annealing process is performed to expand thefirst doping regions 115.

Referring to FIG. 22, a second impurity implanting process (obliqueimpurity implanting process) is performed using the gates GGS, SSG, andMG as masks. The oblique ion implanting process may be performed at asecond angle θ2 in a manner similar to that described above. Theimpurities used in the second impurity implanting process may have thesame conductivity type as in the first impurity implanting process.

To reiterate, the first angle θ1 may be the minimum angle at which theimpurities can be implanted into the active region between the memorygate MG and the adjacent selection gate GSG or SSG. The second angle θ2is based on the distance d2 between the adjacent string selection gatesSSG and SSG′ (or the adjacent ground selection gates GSG GSG′) and theheight h1. In particular, the second angle θ2 is the minimum angle atwhich the impurities can be implanted into the active region between theadjacent string selection gates SSG and SSG′ (or the adjacent groundselection gates GSG GSG′).

Alternatively, an impurity implanting mask (not shown) may be formed tocover the substrate 110 between the selection gates GSG and SSG duringthe ion implantation process. In this case, the active region betweenthe adjacent ground selection gates GSG and GSG′ is exposed by theimpurity implanting mask. The impurities are implanted into the exposedregion of the substrate 110 at an implantation angle θi greater than thesecond angle θ2 and less than 90 degrees (i.e., θ2<θi<90°). The impurityimplanting mask may be a patterned layer of photoresist or spacersformed on sidewalls of the gates GSG, SSG, and MG as disclosed in U.S.Patent Publication No. 2006/0220098.

As a result, the second doping regions 119 are formed at the boundariesbetween the selection channel regions 116 and the selection impurityregions 117.

An annealing process is then performed to expand the second dopingregions 119 to locations below the gates GSG, SSG, and MG.

Thus, the concentration of impurities in at least a portion of each ofthe section channel regions 116 is higher than the concentration ofimpurities in the memory cell region 118.

Another embodiment of a semiconductor device according to the presentinventive concept will now be described below in detail with referenceto FIGS. 1 and 23.

A ground selection gate GSG, a string selection gate SSG, and memorygates MG are disposed on an active region ACT of a substrate 110. Thegates GSG, SSG, and MG are similar to those of the above-describedembodiments. Thus, the substrate 110 has selection channel regions 116below the ground selection gate GSG and below the string selection gateSSG, respectively, a memory cell region 118 between the ground selectiongate GSG and the string selection gate SSG, and selection impurityregions 117 between the adjacent ground selection gates GSG and GSG′ andbetween the adjacent string selection gates SSG and SSG′, respectively.

First doping regions 115 are disposed below the sidewalls of the gatesGSG, SSG, and MG, respectively. Each of the first doping regions 115 mayalso extend to a location below a respective one of the gates GSG, SSG,and MG. Second doping regions 119 are disposed below each of theconfronting sidewalls of the adjacent string selection gates SSG andSSG′ and each of the confronting sidewalls of the adjacent groundselection gates GSG and GSG′, respectively. The second doping regions119 have the same conductivity type as the first doping region 115, butthe concentration of impurities in the second doping regions 119 (secondimpurity concentration) is higher than the concentration of impuritiesin the first doping regions 115 (first impurity concentration).

Thus, the concentration of impurities in at least a portion of each ofthe section channel regions 116 is higher than the concentration ofimpurities in the memory cell region 118.

There is also thus provided a unit memory cell region 118 a thatincludes a unit memory channel sub-region 118 b disposed below onememory gate MG and unit memory impurity sub-regions 118 c at oppositesides of the memory gate MG.

A respective third doped region 164 extends between each of theselection gates SSG and GSG and the memory gate MG adjacent thereto. Thethird doped regions 164 are of a different conductivity type differentfrom that of the first doping regions 115. Thus, in at least one unitmemory cell region 118 a the unit memory channel sub-region 118 b is ofa conductivity type different from that of the unit memory impurityregions 118 c.

Spacers 165 are disposed on sidewalls of the gates SSG, GSG, and MG. Thespacers 165 may fill the spaces between the memory gates MG, but exposeportions of the active region between the adjacent selection gates. Abitline junction impurity region 167 extends in the substrate 110between the string selection gates SSG and SSG′, and a common sourceregion 168 extends in the substrate 110 between the ground selectiongates GSG and GSG′. An interlayer dielectric 170 is disposed on thesubstrate 110 over the gates SSG, GSG, and MG. A bitline contact BC anda common source line CSL extend through the interlayer dielectric 170into contact with the bitline junction impurity region 167 and thecommon source region 168, respectively. A bit-line BL extends along theinterlayer dielectric 170 and intersects and is connected to the bitlinecontact BC.

A method of manufacturing the semiconductor device of FIG. 23 accordingthe present inventive concept will now be described below in detail withreference to FIG. 1 and FIGS. 23 through 25.

Referring to FIGS. 1 and 24, a structure is formed as described above inconnection with FIGS. 20-22. An impurity implanting mask 161 is formedon the structure (shown in FIG. 19). The impurity implanting mask 161has openings 163 that expose regions of the substrate 110 to beimplanted with impurities. More specifically, the impurity implantingmask 161 exposes respective portions of the active region between eachselection gate SSG and GSG and the memory gate MG adjacent thereto. Theimpurity implanting mask 161 may be formed of a layer of photoresist,silicon nitride or silicon oxide.

An impurity implanting process is then performed using the impurityimplanting mask 161. As a result, third doped regions 164 are formed.The impurities used are such that the third doped regions 164 are of aconductivity type different from that of the first doping regions 115.For example, the third doped regions 164 may contain N-type impuritieswhile the first doping region 115 may contain P-type impurities. Theimpurity implanting mask 161 is then removed.

Referring to FIG. 25, spacers 165 are formed on sidewalls of the gatesSSG, GSG, and MG. Using the spacers 165 as masks, are implanted into thesubstrate 110 between the string selection gates SSG and SSG′ andbetween the ground selection gates GSG and GSG′ to form a bitlinejunction impurity region 167 and a common source region 168. The bitlinejunction impurity region 167 and the common source region 168 have thesame conductivity type as the third doped regions 164.

Referring to FIG. 23 again, the interlayer dielectric 170 is then formedon the gates SSG, GSG, and MG. A bitline contact BC is formed in theinterlayer dielectric 170 between the string selection gates SSG andSSG′ as electrically conductively connected to the a bitline junctionimpurity region 167, and a common source line CSL is formed interlayerdielectric 170 between the ground selection gates GSG and GSG′ aselectrically conductively connected to the common source region 168. Abit-line BL is then formed on the interlayer dielectric 170 aselectrically connected to the bitline contact BC.

An electronic system 200 including a semiconductor device according tothe present inventive concept will now be described below in detail withreference to FIG. 26. The electronic system 200 may be used in wirelesscommunication devices such as, for example, personal digital assistants(PDA), laptop computers, portable computers, web tablets, cordlessphones, mobile phones, digital music players, and all other devicescapable of sending and/or receiving data in a wireless environment.

The electronic system 200 includes a controller 210, an input/outputdevice (I/O) 220 (e.g., a keypad, a keyboard, a display or the like), amemory 230, and a wireless interface 240, which are connected through abus 250. The controller 210 includes at least one microprocessor, adigital signal processor, a microcontroller or the like. The memory 230is used to store, for example, commands executed by the controller 210.Also the memory 230 may be used to store user data. The memory 230includes a semiconductor device according to the present invention.

The wireless interface 240 transmits and receives data into and from awireless communication network that is communicating through an RFsignal. For example, the wireless interface 240 includes an antenna, awireless transceiver or the like.

The electronic system 200 may be used in a communication interfaceprotocol of a third generation communication system such as CDMA, GSM,NADC, E-TDMA, WCDAM, CDMA2000 or the like.

A memory system 300 including a semiconductor device according to thepresent inventive concept will now be described below in detail withreference to FIG. 27. The memory system 300 includes a memory device 310for storing large amounts of data and a memory controller 320. Thememory controller 320 controls the memory device 310 to read/writestored data from/into the memory device 310 in response to read/writerequest of a host. The memory controller 320 may constitute an addressmapping table for mapping an address provided from the host 330 (amobile device or a computer system) to a physical address of the memorydevice 310.

As described above, a semiconductor device according to the presentinventive concept includes selection and memory transistors, wherein thethreshold voltage of the selection transistors is higher than that of amemory transistor. To this end, the channel regions of the selectiontransistors have a higher concentration of impurities than the channelregion of the memory transistor. When the present inventive concept isapplied to a flash memory device, leakage current of a string issuppressed to enhance programming reliability of the semiconductordevice.

Although the present inventive concept has been described in connectionwith the embodiment of the present inventive concept illustrated in theaccompanying drawings, it is not limited thereto. It will be apparent tothose skilled in the art that various substitutions, modifications andchanges may be made without departing from the scope and spirit of theinventive concept.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising: providing an active region; forming a string of gatesincluding a string selection gate, a ground selection gate and memorygates between the string selection gate and the ground selection gate;and forming a first doping region of a first type in the active regionadjacent to at least one of the string and ground selection gates,wherein the first doping region has a higher concentration of impuritiesthan a portion of the active region adjacent to the memory gates.
 2. Themethod as set forth in claim 1, wherein the active region is doped byimpurities of the first type.
 3. The method as set forth in claim 1,wherein the forming of the first doping region is performed beforeforming the string of the gates.
 4. The method as set forth in claim 1,wherein the forming of the first doping region is performed by anoblique implantation process.
 5. The method as set forth in claim 1,wherein the forming of the string of gates comprises forming twoneighboring string selection gates, such that a first distance betweenneighboring memory gates is shorter than a second distance between theneighboring string selection gates, and the forming of the first dopingregion comprises determining an angle of implantation based on the firstdistance and the second distance, and implanting impurities into theactive region at said angle of implantation relative to the surface ofthe active region.
 6. The method as set forth in claim 1, wherein thefirst doping region is formed by an oblique implantation process at animpurity-implanted angle of less than 90 degrees relative to the surfaceof the active region.
 7. The method as set forth in claim 1, wherein thefirst doping region is not overlapped with any of the memory gates in afirst direction, the first direction being perpendicular to a surface ofthe active region.
 8. The method as set forth in claim 1, furthercomprising, before the forming of the first doping region, formingsecond doping regions in the active region adjacent to the memory gates,respectively, wherein the second doping regions are doped by impuritiesof the first type with a lower concentration than the first dopingregion.
 9. The method as set forth in claim 8, further comprisingforming third doping regions in the active region between the stringselection gate and a memory gate among the memory gates adjacent to thestring selection gate and between the ground selection gate and anothermemory gate among the memory gates adjacent to the ground selectiongate, wherein the third doping regions are doped by impurities of asecond type which is different from the first type.
 10. The method asset forth in claim 8, wherein the first doping region is formed to bedeeper than the second doping regions.
 11. The method as set forth inclaim 10, wherein the first doping region is formed to be verticallyoverlapped with the string and ground selection gates and to be extendedoutwardly from the string of the gates, and the second doping regionsare formed to be disposed at the active region between the memory gates,between the string selection gate and a memory gate among the memorygates adjacent to the string selection gate and between the groundselection gate and another memory gate among the memory gates adjacentto the ground selection gate and to be extended outwardly from thestring of the gates.
 12. The method as set forth in claim 11, whereinthe second doping regions are formed to be absent from the active regionbelow centers of the memory gates, the string selection gate and theground selection gate.
 13. The method as set forth in claim 12, whereinthe second doping regions are formed to be absent from the active regionbelow centers of spaces between the memory gates, between the stringselection gate and a memory gate adjacent to the string selection gateand between the ground selection gate and another memory gate adjacentto the ground selection gate.
 14. The method as set forth in claim 3,wherein the active region includes selection gate regions where thestring and ground selection gates are disposed and a memory gate regionwhere the memory gates are disposed and selection gate regions betweenthe selection gate regions, and the forming of the first doping regioncomprises: forming a mask pattern to cover the memory gate region and toexpose selection gate regions on the active region; and performing animpurity-implantation process using the mask.
 15. The method as setforth in claim 14, wherein the impurity-implantation process is anoblique implantation process, and the first doping region is formed tobe extended under the mask pattern.
 16. The method as set forth in claim1, wherein at least one of the memory gates is formed to include a firstmemory insulating layer, a charge storage layer, a second memoryinsulating layer, and a conductive layer which are sequentiallydisposed.